With the development of science and technology, a variety of electronic products emerge and almost become an indispensable part in daily life. With advantages of high energy density, long cycle life, environmental friendliness and reproductivity, lithium ion batteries have been widely used in various electronic products.
Generally, lithium secondary batteries are formed through setting an electrode assembly and electrolyte in a battery shell, and sealing the battery shell. Electrode units used in the electrode assembly may be categorized into convolution (winding)-type electrode units, a lamination-type electrode units, and folding-type electrode units according to their structure.
In the related art, a polypropylene layer of a laminated aluminum film is generally used to isolate an anode current collector in an anode sheet. Since the requirements of energy density of an electric roll at the market become higher and higher, a thickness of the polypropylene layer of the laminated aluminum film, and a thickness of the anode current collector become smaller. In one aspect, an anti-puncture strength of the thinned polypropylene layer becomes lower. In another aspect, since the anode current collector of the lithium ion battery is a copper foil, with the restriction of process conditions in the related art, burrs may exist on an end edge of the copper foil, which may cause the case where the burrs on the end edge of the anode puncture a separator and a laminated aluminum film under extreme conditions. However, in a lamination-type or stacking-type lithium ion electric roll, the edge of the thinned anode current collector will become sharper, which increases the probability that the polypropylene layer of the laminated aluminum film is punctured by the anode current collector.
After the polypropylene layer of the laminated aluminum film is punctured, which may cause battery leakage, and more seriously, may result in that the anode is conducted with the aluminum foil layer via contact. In this case, an electrochemical reaction may occur and thus the polypropylene layer of the laminated aluminum film may be subjected to corrosion, which also causes battery leakage and corrosion.